Method for gluing, device for carrying out the method and glue composition for use in the method

ABSTRACT

Methods for gluing a pair of surfaces are disclosed including preparing a glue from a polymer in the form of a powder, the glue having a melting temperature of up to about 100° C. and being curable by electromagnetic radiation, applying the powder in a dry state to at least one of the two surfaces, heating a region proximate to at least one of the surfaces whereby the powder melts but does not cure, subjecting that surface to electromagnetic radiation to initiate curing of the powder, and joining the two surfaces together prior to completion of curing whereby the two surfaces adhere to each other by means of the tackiness of the glue and are maintained together by the subsequently cured glue. Apparatus for gluing the two surfaces together are also discussed, as are glue compositions for use therein.

TECHNICAL FIELD

The present invention relates to a method for gluing and a device and aglue composition intended to be used for the gluing according to themethod.

STATE OF THE ART

The agglutination of surfaces requires a substance, the glue, which maybe brought to a first, tacky state, so that the glue adheres to thesurfaces which are to be joined. When the surfaces have been united withthe glue between them, the glue is converted to a more or less solidstate, whereby the glue joint obtains its final tenacity towards ruptureof the joint. The difference in cohesive force between the first and thesecond state may be extremely different.

Certain glues, such as urea-formaldehyde resin glues, have a very lowcohesive force in the first state but provide a strong joint when theglue has hardened. Other glues, such as contact adhesives, provide ajoint of a considerable strength immediately after the surfaces havebeen joined, but thereafter the strength of the joint does not increasevery much.

The conversion from the first to the second state may, depending on thetype of glue, occur in many different ways. In the first state, manyglues are a tacky mass, which solidifies by means of the evaporation ofa solvent. Such solvents are often non-environmentally friendly;volatile hydrocarbons are common. Other glues are hard at roomtemperature and are converted to a tacky state by heating. However, theutilization of a phase change in this way will normally give limitedstrength to the finished glue joint. In many cases, furthermore, it isnot rational to work with a glue which has to be kept heated during thegluing operation. There are additional glue types and systems, whichstart from natural products or from more conventional chemical productsor systems.

Another branch of glue technology is represented by polymeric materials.Thermoplastic systems, which are brought to a tacky state by heating andto a solid state by cooling down, do not in principle differparticularly from conventional systems with a corresponding processcourse. Systems with thermosetting plastics, on the other hand,represent a special branch of glue technology. Such plastics may begiven a plurality of states, from thinly fluid, through viscous tackymasses, to a solid state as foils, which are converted to a tacky stateby heating during the gluing process itself. After the gluing surfaceshave been brought together, the glue is, by means of curing of theplastic, converted to a solid state from the first state with a more orless fluid consistency. This requires initiation of the curing, whichmay occur in different ways depending on the type of thermosettingplastic and its components. An addition of a chemical hardener is oftenused which, however, has the disadvantage that the gluing process has tobe performed within a limited time and that difficulties arise when itcomes to cleaning the utilised vessels and tools if the plastic isallowed to cure on these.

Thus, there are both disadvantages and limitations with the use ofthermosetting adhesives since, in many cases, they may be less rationalto use in industrial production than other gluing systems. In manyrespects, however, they possess superior properties when it comes to thestrength of the glue joint, long lifetime towards ageing and smallinfluence on the strength when heated within the temperature rangeduring use. A further advantage is that the curing does not give anyemission of environmentally harmful substances, which is the case whenglues with solvents are concerned.

SUMMARY OF THE INVENTION

The present invention has as an object to provide a gluing method, whichstarts from a thermosetting resin glue, which is also comprised by theinvention. The object is to achieve a method which is very rational tocarry out in industrial production, whereby the glue in question is veryconvenient to handle. At the same time the earlier mentioned advantages,which are associated with thermosetting adhesives, are gained, namelyhigh strength and heat resistance of the glue joint and the absence ofemissions of substances which are dangerous to the environment duringthe gluing.

This is achieved since the glue is manufactured in a pulverous state andmay be in this state right up to the start of the gluing process. Theentire handling, including the application of the pulverulent glue, mayconsequently be done with a dry product and, as such, no storage vesselsor tools for the handling and application of a tacky mass are required,so that a very rational method thereby is obtained.

DESCRIPTION OF THE DRAWINGS

The method and the glue according to the invention are described in thefollowing. Thereby, reference is made to two specific gluing processeswhich are illustrated in attached drawings by schematic representationsof each process equipment, as is shown in FIGS. 1 and 2, respectively.

PREFERRED EMBODIMENT

The description of methods according to the invention will start with anaccount of a gluing process performed in process equipment which isschematically shown in FIG. 1. In this case, the process relates to thegluing of a film to steel plates. The resulting product is panelsintended to be used as a wall covering. One extensive field of use is asa wall covering in ships, train carriages etc., and also in buildings,especially in prefabricated ones. In the drawing, reference numeral 1denotes a conveyor belt on which steel plates 2, in a consecutive order,may be conveyed forwards, from left to right in the drawing. The platesthereby pass a laminating mill 3. This comprises, seen in the directionof transport, a glue application station 4, a heating station 5 and alaminating station 6.

The application station 4 for the pulverulent glue is herein shown toconsist of one or several powder spray guns 8, arranged forelectrostatic charging of the powder. In order to cover the full widthof the plates 2, one or several of the guns may be arranged for movementback and forth in the transverse direction of the plates. Hereby, it isassumed that the plates are electrically conductive, they may forinstance be made of steel or aluminium, and earthed, which is achievedby the plates lying on the conveyor belt 1 which in turn is connected toearth. The guns 8 are supplied with powder and pressurized air for thespraying via one or several conduits 9.

The heating station 5 is hereby shown as a hood 12 over the conveyorbelt. It is arranged for convection heating by means of the supply ofheated air through a conduit 13.

The laminating station 6 is supplied with the film which is to be gluedto the plates from a roll 15 which is rotatably suspended on a shaft 16.A film web 17 runs from the roll to the nip between the plate 2, whichis to be laminated, and a press roller 18. After the press roller therefollows a film cutting member 19.

The laminating plant is very schematically shown and described as oneembodiment amongst many alternative embodiments. Thus, the plant may bearranged for continuous lamination of a long plate web, which is fedfrom a roll and which is cut into suitable lengths for use after thelamination. The pulverulent glue may be applied in another way than byspraying even if this is an advantageous method. The heating may,besides by hot air, be done by infra-red heat or contact heating of theplates. Also heating by means of induction is a possible alternative.

In the shown embodiment, the plates 2 are gradually advanced on theconveyor belt 1 and firstly meet the glue application station 4 at whichthe surface of the plate is sprayed with the electrically charged gluepowder. A layer of this sticks to the surface of the plate which isearthed, and is retained thereon by electrostatic forces. In the heatingstation 5 the plate is exposed to the hot air, which should hit theplate at a low speed in order not to blow the powder away. By means ofthe heating, the plate should reach a temperature of 250 ° C. before itreaches the spot where the film web 17 is pressed into contact with theplate by the press roller 18. When the plate has passed the pressroller, the film web is cut at 19, which may be done by means ofcutting/shearing or by means of heat which melts the film along a line.At the same time, a new plate is brought in beneath the roller 18 andthe operation is repeated.

The earlier mentioned temperature is so adapted that the glue powder ismelted so that it sticks to the two united surfaces. Immediatelythereafter, the powder, which as earlier mentioned consists of athermosetting plastic, is cured. A temperature of 250° C. has proved tobe applicable for the composition which will be described in thefollowing. At the same time, the temperature allows lamination withoutthe film being damaged. Here, it is namely assumed that the film is aplastic film with a melting temperature which is just above said value.When material compositions other than a plastic film are concerned, suchas PVC laminated on a metal plate, it may be necessary to choose a lowertemperature in order not to damage the materials. In such cases, thepowder composition must also be adapted to melting and curing at such alower temperature.

Certain method steps, which represent the principles of the method, areevident from the described embodiment. These steps are:

1. Preparing a glue composition which completely, or to a considerableextent, consists of an uncured, thermosetting plastic, which in thisstate and in a temperature range around about room temperature, adopts asolid state, while at a raised temperature, for instance 80-300° C., bymeans of melting it forms a tacky mass with adherence to surfaces whichare to be glued.

2. Preparing the glue composition for use, to a dry powder with thecomposition so adapted that the powder can be given an electrostaticcharge.

3. Preparing the gluing surfaces in order to provide for the adhesion ofthe glue to these. The surfaces should of course not be dusty, dirty orgreasy, something which in general is valid for all gluing. In certaincases, it may also be necessary to remove traces of oxide, rust orembers from the surfaces. Despite such basic pre-treatment, it may beadvantageous for the strength of the glue joint if the surfaces arepre-treated. When steel plate is the substrate, chromating has beenshown to be of value. In other cases, the application of a primer may beconvenient. This may contain an organic component in order to obtain agood affinity to the thermosetting plastic in the glue. Forenvironmental reasons, solvent-based coatings should be avoided, wherebywater-based compositions may be an alternative. Another alternative maybe that the primer coating is also done by powder coating.

4. The powder glue is given an electrostatic charge. The purpose ispartly to give the powder particles a uniform distribution in the roomduring the application process so that the powder particles coat thegluing surface with an even layer, and partly in order to get the powderparticles to adhere to the glue surface until such heating has occurredthat the powder sticks to the gluing surface. The last mentioned effect,that the powder particles should be retained on the gluing surface byelectrostatic forces, presupposes that a difference in potential may bemaintained between the charged powder and the gluing surface. Asmentioned earlier, this may occur if the substrate is electricallyconductive and earthed during the application. When non-conductiveobjects, such as chipboard as a substrate, are concerned it may benecessary to resort to methods other than the one mentioned, forinstance coating the surface of the substrate with a conductive varnish,moistening the surface of the substrate or pre-heating to such atemperature that the powder particles adhere by melting in the interfacetowards the substrate.

5. Applying the glue powder on at least one of the surfaces which are tobe agglutinated. Application by means of spraying from guns which givean electrostatic charge before the spraying with pressurized air, is awell-tried and advantageous method.

6. Heating to such a temperature that the powder melts in order to stickto the gluing surfaces. As mentioned in the example, the heating mayoccur by means of the object, in this case the plate, being heated tothe required temperature so that the melting temperature of the powdermay be reached and maintained in connection with the application of thenon-heated film. In other cases it may be convenient to heat bothcomponents which are to be joined. When objects having a larger mass areconcerned, such as boards of a larger thickness, through-heating doesnot have to be practised but only surface-heating. Thus, heating bymeans of infra-red radiation may be a suitable method, possibly incombination with hot-air heating. Objects which conveniently should bethrough-heated may be heated before the gluing, for instance in an oven.

7. Joining the gluing surfaces while maintaining such a temperature thata curing of the powder takes place in direct connection to the joining.The means for obtaining a strong glue joint is a joining with a raisedsurface pressure, and of course while ensuring that no air cushion isformed between the surfaces. A lengthy pressing together of the surfacesis, however, not required. If the appropriate parameters for the gluingmethod have been chosen, a very rapid curing of the thermosettingplastic in the powder is obtained.

After this description of the method, both in a specific embodiment aswell as in its general form, a description of a preferred gluecomposition now follows.

The main components of the glue should be one or several polymers orco-polymers of a thermosetting type, systems for initiation of thethermosetting and whenever applicable fillers, particularly applicablewhen uneven surfaces, which do not come into complete contact with eachother, are concerned, pigments for colour adjustment, especially atjoints where the glue partly becomes openly visible or perceptible bymeans of a certain transparency of the substrate, and additives forincreasing the strength of the glue joint and/or in order to facilitatethe gluing process. Below, components which are useful in this contextare listed.

Examples of Components

    ______________________________________                                        Thermosetting plastics:                                                       Polyester (hydroxy-functional polyester)                                      Polyester (acid-functional polyester)                                         Acrylic (hydroxy-functional polyester)                                        Acrylic (acid-functional acrylate)                                            Acrylic (epoxy-functional acrylate)                                           Epoxy (Bisphenol-A type)                                                      Epoxy (Novolac-type)                                                          Hardeners:                                                                    Blocked IPDI derivative                                                       IPDI-uretidione                                                               TDI derivatives                                                               TMXDI and other polyisocyanates                                               Triglycidylisocyanurate                                                       Melamines                                                                     Glycouriles                                                                   Hydroxy-alkylamides                                                           Glycidylbased compounds                                                       Derivatives of dicyandiamide                                                  Modified aromatic and aliphatic polyamines                                    Polyphenoles                                                                  Acid anhydrides                                                               Amino resins (melamine, benzoguanamine, glycoluryl)                           Other additives:                                                              Additives:                                                                    Accelerators, Benzoin, Flow additives, Wetting                                agents, Flatting agents, Waxes, Adhesion promotors                            Fillers:                                                                      Inorganic compounds such as BaSO.sub.4, CaCo.sub.3, CaSiO.sub.3,              Dolomite, Talc, Mica                                                          Pigments:                                                                     Inorganic, organic, TiO.sub.2                                                 ______________________________________                                    

When composing a specific glue, the components suitable for theprevailing conditions are selected from the conceivable components ineach group. Accordingly, determining factors are the adhesion betweenthe gluing surfaces in question and the glue, the physical shape of thesurfaces, the possibility of a tight or less tight fit-up, smoothnessetc., possible absorption of the substrates such as when fibrousmaterials are concerned, permissible melting and curing temperature,possible limits are 80° and 300° C., desired curing time wherebypossible times lies within the range 5 seconds to 5 hours, andrequirements concerning the agglutinated objects, such as strength ofthe joint, resistance to fatigue, flexibility from hard as glass toelastomer-like and resistance to both low and high temperatures.

As is evident, one or several thermosetting plastics are selected forthe binder system, from one or several of the groups polyester, acrylicor epoxy with a thermo-initiating hardener adapted for curing at apredetermined temperature and curing time. Depending on thecircumstances, important additives are accelerators when a shortenedcuring time is desired, flow additives in order to obtain a suitableviscosity when pressing together the gluing surfaces, thus additiveswhich are dependent on the process requirements, and wetting agents andadhesion promotors in order to achieve increased adhesion which isparticularly important for voidless, shiny materials which are difficultto wet, for instance glass. Pigments as well as flatting agents are asearlier mentioned, in the main, based on appearance requirements. Thefillers are not chemically active in this context, but are importantwhere a filling of cavities in the joint is necessary.

The strength of a glue joint depends on the tenacity of the glue and itsadhesion to the gluing surfaces. When a thermosetting plastic isconcerned, the adhesion is normally the most critical. In the presentcontext, the co-polymer Methyl-vinylester--Maleic anhydride has beenfound to be an effective adhesion promotor, particularly when polyesteras a binder system is concerned.

Specific for the described and disclosed method is that the pieces whichare to be joined may be heated to the temperature which is required forthe curing of a thermosetting adhesive, normally about 200° C. This maybe realized without difficulties in the process which has beenmentioned, namely laminating, where both parts are in the form of thinlayers, which can easily be through-heated by the supply of heat fromoutside. Since at least one of the layers is pliable, heat can easily besupplied in the gap which is formed between the two surfaces, if thepliable layer is successively, conveniently by rolling, applied onto thepiece which is to be laminated. Such lamination does not have to implythat two elongate webs or at least one elongate web is necessary, as inthe described process, and provides the possibility of a continuousprocess. It is also possible with individual pieces of laminating layersand carrier layers if the laminating layer is kept bent upwards and issuccessively pressed down against the carrier layer.

There are, however, work pieces and conditions in which the describedprocess cannot be practised. This is especially valid for stiff piecessuch as hard plates, which cannot be joined successively while beingbent up, and pieces which are difficult to heat to the curingtemperature of a thermosetting adhesive. The latter limitation may bedue to the fact that the material of one or both the pieces does notallow a heating to the curing temperature since they may melt or bedeformed, or because the mass is so large, when thick pieces areconcerned, that a through-heating would be far too energy-consuming.Therefore, an alternative method will be described herein, which enablesgluing with a pulverous thermosetting plastic also during saidconditions. Thus, reference is made to FIG. 2. The method is based onpreparing the glue to have a low melting temperature, which is adaptedto the temperature endurance of the work pieces. By means of a suitablecomposition of the glue, a melting point below 100° C. may be reached.This temperature is sufficient only in order to get the glue into amelted and sticky state, but not in order to cause it to cure. Instead,the glue is composed with a curing system which gives curing by means ofelectromagnetic radiation, preferably ultraviolet radiation(UV-radiation). Also, other electromagnetic radiation such as gammaradiation may initiate curing if the curing system of the glue isdesigned therefor.

Curing by radiation occurs in a very short time, times down to one or afew seconds may be reached, which is considerably faster than whenthermosetting is concerned. Since such radiation cannot reach into theglue joint, when non-transparent work pieces which have been joined areconcerned, the irradiation must take place while the work pieces areseparated. Consequently, the curing time of the glue must be adapted sothat the work pieces can be joined before curing begins. Theserequirements may be met by means of a method according to the followingspecification:

1. Preparation of the glue composition from an uncured thermosettingplastic so that it, at a moderately raised temperature assumed to bebelow 100° C., by melting from a solid state forms a tacky mass withadhesion to the surfaces which are to be glued. The glue composition isarranged not to cure at said temperature but to cure when exposed toelectromagnetic radiation such as UV-radiation.

2. Preparation of the glue composition as a dry powder which may begiven an electrostatic charge.

3. Preparation of the gluing surfaces in order to provide for theadhesion of the glue thereto.

4. Heating of at least the surface layer of at least one of the objectswhich are to be agglutinated to such a temperature that, when powder isapplied, it reaches said temperature level where melting to a tackystate occurs. Since the applied powder might not completely adopt thetemperature of the surface, and since a certain cooling may take place,it may be presumed that the surface temperature must be a little higherthan the temperature at which the powder melts, but not so high thatthermal curing of th e plastic arises.

5. Application of the glue powder on the surface or at least on one ofthe heated surfaces. Thereby, the powder is preferably provided with anelectrostatic charge for distribution of the powder. If the surfaceshave another potential or polarity in relation to the powder, thedistribution of the powder may at the same time, to a great extent, belimited to such surfaces.

6. Exposing the applied and, by means of heat conduction from the coatedsurface, melted powder to electromagnetic radiation so that curing isinitiated. The powder must, however, be adapted so that curing does notbegin at once and before the next moment has been performed.

7. Joining the gluing surfaces under compression before curing takesplace (see above).

The powder which is to be used is primarily of the same type which hasbeen described for the thermo-setting method. However, the powder mustbe adapted for radiation-curing by containing curing initiators or sucha polymer system, which in itself is initiated by the chosen radiation.Particularly for curing with UV-radiation and with a powder which meltsat said low temperature, the following composition may be adopted:

The main component of the powder is to 50-<100% an unsaturatedpolyester, amorphous or crystalline. Furthermore, a hardener ispreferably included in order to obtain increased cross-linking duringthe curing stage. This hardener may be an aromatic urethane diacrylateoligomer, a triacrylate of trihydroxy-ethylisocyanurate, a vinyl ester,an oligomer acrylourethane or something similar, to 15-50%. An additionof a photoinitiator is required in order to initiate the curing stage.This addition may vary between 1-3%. For a clear varnish, it isadvantageous to use a 1-hydroxy-cyclohexyl-ketone as a photo-initiator,and for white pigmented systems2,4,6-trimethylbensoyl-diphenyl-phosphineoxide may be used. This ishowever only specified as an example and completely differentphoto-initiators may be needed for particular purposes. An addition of alevelling agent is also presumed. 1-3% of this is recommended. As alevelling agent e.g. acrylates may be used.

Basic recipe for a composition which provides good levelling-out aftermelting at low temperatures and a good solvent resistance.

Unsaturated polyester 70-85%

Hardener 15-30%

Photo-initiator 1-3%

Levelling agent 1-3%

The melting temperature of the powder should, at the most, be 80-90° C.in order to ensure that a wooden component is not damaged during themelting phase. The melting should take place by means of IR-heat or acombination of IR- and convection heat. This implies that the meltingphase, at such relatively high temperatures as these, does not have tobe in progress during an especially long time since IR rapidly heats thewooden components to the desired temperature. A few minutes may beassumed to be what it is needed, but is very much dependent on thematerial which is to be coated. Certain wooden materials are verysensitive to a rapid heating and experience a strong degassing, whichmight entail that a slower and more careful heating method must beselected.

By way of example, a device for carrying out the described method isshown in FIG. 2. Here it is assumed that two stiff slabs 22 and 23 areto be agglutinated. The slab 22 is placed at the bottom and on a fixedtable 24. The slab 23 is supported by a plate 25 by means of suctioncups 27, which are under negative pressure since they are connected to asuction pump by means of conduits 28 (only one suction cup with aconduit is shown in the drawing).

The plate 25 is supported by an yoke 29, which in turn is supported by apower device 30 such as a hydraulic cylinder (only partly shown). Bymeans of this device, the slab 23 may be kept in a raised position abovethe slab 22 so that a space is formed between the opposing surfaces. Bymeans of the power device 20, the slab 23 may be lowered and pressedagainst the slab 22 with said surfaces pressed against each other.

Rails 32 travel along both sides of the table 24 (only the ends areshown). A wagon 33 may run on these rails. It is exposed on both sidesto directed rays 34 for heat radiation, infrared light. A feedable cable(not shown) for current supply to the rays is arranged. A second wagon36 is also arranged to run on the rails. It supports a number of powderspray nozzles 37 which are arranged so that the complete surface of thelower slab 22 may be coated with powder. It is also conceivable that theupper surface be coated with powder by means of spray nozzles which aredirected upwards. As mentioned earlier, it is advantageous if the powderis electrostatically charged and thereby receives a uniform distributionbefore it reaches the surface. It has also been mentioned that if thesurfaces may obtain another potential than the powder, they will attractthe same, so that the distribution outside the surfaces which are to becoated is limited.

Furthermore, the device is provided with radiators for ultravioletlight, which are marked with circles 39. The intention is that theUV-light shall reach the surfaces which are coated with powder. Sincethe space between the surfaces of the slabs may be relatively narrow, agood light distribution must be provided. This may be achieved by meansof a plurality of radiators around the slabs or, alternatively, theradiators may also be located on a wagon which may be moved on the rails32.

Gluing in the described device takes place such that after the slabs 22and 23 have been supplied and the slab 23 has been lifted by negativepressure inside the suction cups 27, the wagon 33 with the heatradiators 34 is passed through the space between the opposing surfacesof the slabs. The intensity of the heat rays and the speed of the wagonare so adapted that at least the surface layer of the slabs receivesheating to the earlier mentioned temperature level. The heating may besupported by means of blowing in heated air; the device for this is,however, not shown. On the whole, the heating is adapted to the natureof the objects which are to be agglutinated, and to the extension oftheir surfaces etc. In certain cases, solely heating or heat radiationis to be preferred. In other cases, convection heating by means ofheated air is to be preferred, and in many cases a combination isprobably the most convenient.

When the surfaces have obtained a sufficient heating, the wagon 36 isbrought into the space between the slabs and at least one surface iscoated with powder. This will then melt and thus adhere to the coatedsurface. Therefore, it is also possible to coat the surface facingdownwards, without the powder falling off, even if retention by means ofelectrostatic forces would not be utilized.

The surfaces are now coated with the thermosetting plastic glue whichhas adopted a melted and tacky state. While this state still ismaintained, the glue-coated surfaces are subjected to the ultravioletradiation by means of the radiators 39 or, as earlier mentioned,radiators on an additional wagon. This must be done very quickly so thatthe gluing surfaces may be joined by means of activation of the powerdevice 30 with the plate 25 being lowered and compressing the two slabs.After initiation by the radiation, the curing namely starts rapidly andtherefore a rapid sequence of the irradiation and the compression isrequired.

The embodiment described in connection with FIG. 2 only constitutes anexample. It must be adapted to different types of objects and surfaceswhich are to be agglutinated. Important are, however, the main elementsof heating, coating with powder and melting of the same, and irradiationin order to initiate the curing and immediately thereafter pressing thesurfaces together.

The described device only shows an example of how the method in itssecond embodiment may be carried out with the use of UV-curing powder.The method in this form may for instance also be applied to a gluingcorresponding to the first embodiment shown in FIG. 2. If the ingoinglamination materials are not suitable to heat to the temperature forthermo-setting, one or both layers may be heated to the lowertemperature. The powder is applied to at least one of the layers beforethe layers meet, so that curing starts at a distance from the nip nearby the roller. Within this distance the curing is initiated by emittinga focused band of UV-radiation or other applicable electromagneticradiation.

What is claimed is:
 1. A method for gluing first and second surfacetogether comprising preparing a glue comprising a polymer in the form ofa powder, said glue having a melting temperature of up to about 100° C.and being curable by electromagnetic radiation applying said powder in adry state to at least one of said first and second surfaces, heating aregion proximate to said at least one of said first and second surfaceswhereby said powder melts but does not cure, subjecting said at leastone of said first and second surfaces to electromagnetic radiation inorder to initiate curing of said powder, and joining said first andsecond surfaces together prior to completion of said curing of saidpowder whereby said first and second surfaces adhere to each other bymeans of the tackiness of said glue and are maintained together by saidsubsequently cured glue.
 2. The method of claim 1 wherein said glue hasa melting temperature of between 60 and 100° C.
 3. The method of claim 1wherein said electromagnetic radiation comprises ultraviolet radiation.4. The method of claim 1 including heating said at least one of saidfirst and second surfaces by heat radiation or convection by heated airprior to said applying of said powder.
 5. A method for gluing first andsecond surfaces together wherein said first surface comprises a flexiblesurface comprising preparing a glue comprising a thermosetting polymerin the form of a powder, bending said first surface in a manner withrespect to said second surface whereby said first and second surfacesare successively pressed against each other to form a nip therebetween,applying said polymer in a dry state to at least one of said first andsecond surfaces at said nip between said first and second surfaces andon said at least one of said first and second surfaces displaced fromsaid nip where said first and second surfaces are separated from eachother, heating said glue to a tacky state whereby said glue adheres tosaid at least one of said first and second surfaces, and curing saidglue by applying electromagnetic radiation to said at least one of saidfirst and second surfaces when said surfaces are pressed together. 6.The method of claim 5 wherein said applying of said polymer in said drystate comprises applying said powder in an electrostatically chargedstate, and including maintaining a potential or polarity difference insaid at least one of said first and second surfaces whereby said powderis retained by means of electrostatic forces until said powder melts tothereby obtain adhesion therewith.
 7. A composition of matter for use inthe method of claim 12 comprising a glue having a melting temperature ofup to about 100° C. and being curable by means of electromagneticradiation and including an adhesion promoter comprisingmethylvinylether-maleic anhydride.
 8. The composition of matter of claim7 wherein said melting temperature is between about 60 and 100° C. 9.The composition of matter of claim 7 wherein said electromagneticradiation comprises ultraviolet radiation.
 10. The composition of matterof claim 7 wherein said glue comprises at least one polymer, aphotoinitiating system whereby said polymer can be cured by means ofultraviolet radiation, and a leveling agent to provide said glue withsaid melting temperature.
 11. The composition of matter of claim 10wherein said at least one polymer comprises unsaturated polyester in anamount of between about 70% to close to 100% of said at least onepolymer and including a hardener, and wherein said photoinitiator ispresent in an amount of between about 1% and 3% and said leveling agentis present in an amount of between about 1% and 3%.
 12. Apparatus forgluing first and second surfaces together with a glue comprising apolymer in the form of a powder comprising holding means for maintainingsaid first and second surfaces separated by a predetermined gap fromeach other and for pressing said first and second surfaces against eachother, heating means for heating at least one of said first and secondsurfaces, powder application means for applying said powder in a drystate to said at least one of said first and second surfaces radiationmeans for subjecting said at least one of said first and second surfacesto electromagnetic radiation in order to initiate curing of said powder,and activation means for activating said holding means to press saidfirst and second surfaces against each other whereby said first andsecond surfaces adhere to each other by means of the tackiness of saidglue and are maintained together by said subsequently cured glue. 13.The apparatus of claim 12 wherein said heating means comprises means forheating said at least one of said first and second surfaces by means ofheat radiation or convection.
 14. The apparatus of claim 12 wherein saidelectromagnetic radiation comprises ultraviolet radiation.
 15. Theapparatus of claim 12 wherein said heating means comprises mobileheating means whereby said mobile heating means can be moved within saidpredetermined gap, and wherein said powder application means comprisesmobile powder application means whereby said mobile powder applicationmeans can be moved within said predetermined gap.